> I just wanted the shell, not the whole thing

You should post it to suckless.  I recall a thread years ago discussing what
the ‘official’ shell of the suckless project ought to be.  Rc went completely
unmentioned for at least about half of the thread, although they can’t
possibly have been unaware of it... They either want to avoid p9p as a
dependency, or else can’t live without the usual interactive features
of Linux shells.

Now they have no excuse.

As long as we’re discussing Linux stuff in shells, I think the new shell
mpsh[1] has a neat way to set prompt, neat because the mechanism
can also be used to do those variables like OLDPWD that /bin/bash has
built-in knowledge of.
(I wonder what the security implications might be.)

[1] https://www.cca.org/mpsh/docs-05.html

-Morrow